Quasi-resonant auto-tuning controller

ABSTRACT

A quasi-resonant auto-tuning controller includes a zero-voltage crossing detection circuit and a valley tuning finite-state machine having a look-up table. The zero-voltage crossing detection circuit receives a reference voltage and receives an auxiliary signal from an auxiliary winding. The zero-voltage crossing detection circuit produces a comparison signal having pulses when the auxiliary signal is less than the reference voltage. The valley tuning finite-state machine produces a divided pulse width based on the comparison signal, stores the divided pulse width of each pulse in the look-up table, determines, from the comparison signal, that the auxiliary signal is less than the reference voltage, waits a time period corresponding to the divided pulse width stored in the look-up table if the auxiliary signal is less than the reference voltage, and produces a valley point signal after waiting the time period.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/022,034, filed Sep. 15, 2020, which is a continuation of U.S. patentapplication Ser. No. 16/663,626, filed Oct. 25, 2019, which claims thebenefit of priority to U.S. Provisional Application No. 62/833,076,filed Apr. 12, 2019, all of which are incorporated by reference hereinin their entirety.

BACKGROUND

Flyback converters are common in modern power supplies and are utilizedin both alternating current (“AC”) to direct current (“DC”) conversion,and DC-to-DC conversion with galvanic isolation between the input andoutputs of the power supply. In general, a flyback converter is a powerconverter having an inductive device that is split to form a transformerwhich provides the galvanic isolation. In general, a flyback converterhas a primary-side and secondary-side, where the primary-side of theflyback converter includes a switch (such as, for example, a transistor)and the secondary-side includes another switch (such as, for example, adiode) to rectify the current produced by the secondary-side of theflyback converter. In operation, flyback converters generally operate ina switched mode that periodically turns on and off the primary-sideswitch (“main switch”) that supplies current to the inductive device.

In general, power losses in a flyback converter may include conductionlosses, as well as switching losses, Such power losses may reduce theefficiency of the flyback converter, and in turn, generate heat thatcauses the temperature of the flyback converter to approach and/orexceed the peak operating temperature for the flyback converter.Consequently, power losses in the flyback converter may adversely affectthe efficient and/or safe operation of the flyback converter. Tomitigate some of such power losses, flyback converters may be operatedin a quasi-resonant switching mode to reduce switching losses at themain switch and resultantly increase the efficiency of the flybackconverter and lower the operating temperature of the main switch.

A quasi-resonant oscillating signal produced by inductances andparasitic capacitances of the flyback converter generally includes peaks(local voltage maxima) and valleys (local voltage minima), the valleyscorresponding to times when the drain voltage of the main switch is aminimum value. Generally, quasi-resonant switching flyback convertersuse a controller device or circuit to control the operation of theswitches so as minimize switching losses by turning the switches on whenvalleys are present in a quasi-resonant signal.

SUMMARY

In some embodiments, a quasi-resonant auto-tuning controller includes azero-voltage crossing detection circuit and a valley tuning finite-statemachine having a look-up table. The zero-voltage crossing detectioncircuit is configured to receive a reference voltage and to receive anauxiliary signal from an auxiliary winding. The auxiliary signalincludes multiple oscillation ripples, and each oscillation ripple ofthe multiple oscillation ripples has a peak point and valley point. Thezero-voltage crossing detection circuit produces a comparison signalthat includes multiple pulses when the auxiliary signal is less than thereference voltage. Each pulse of the multiple pulses has a pulse widththat corresponds to a half-period of an oscillation ripple of themultiple oscillation ripples. The valley tuning finite-state machine isconfigured to determine the pulse width of each pulse of the multiplepulses of the comparison signal and produce a divided pulse width fromeach pulse width. The divided pulse width corresponds to aquarter-period of the oscillation ripple. The valley tuning finite-statemachine stores the divided pulse width of each pulse in the look-uptable, and determines, from the comparison signal, that the auxiliarysignal is less than the reference voltage. The valley tuningfinite-state machine waits a time period that corresponds to the dividedpulse width stored in the look-up table if the auxiliary signal is lessthan the reference voltage and produces a valley point signal afterwaiting the time period.

In some embodiments, a method involves receiving a reference voltage andreceiving an auxiliary signal from an auxiliary winding of a flybackconverter. The auxiliary signal includes multiple oscillation ripples.Each oscillation ripple of the multiple oscillation ripples has a peakpoint and valley point. A comparison signal is produced, the comparisonsignal including multiple pulses when the auxiliary signal is less thanthe reference voltage. Each pulse of the multiple pulses has a pulsewidth that corresponds to a half-period of an oscillation ripple of themultiple oscillation ripples. The pulse width of each pulse of themultiple pulses of the comparison signal is determined. A divided pulsewidth is produced from each pulse width, the divided pulse widthcorresponding to a quarter-period of the oscillation ripple. The dividedpulse width of each pulse is stored in a look-up table. The methodfurther involves determining, from the comparison signal, that theauxiliary signal is less than the reference voltage and waiting a timeperiod that corresponds to the divided pulse width stored in the look-uptable if the auxiliary signal is less than the reference voltage. Avalley point signal is produced after waiting the time period.

In some embodiments, a primary-side controller of a flyback converterhaving a main switch includes a quasi-resonant auto-tuning controller insignal communication with an auxiliary winding. The quasi-resonantauto-tuning controller is configured to produce a valley point signalfrom an auxiliary signal produced by the auxiliary winding. Amixed-signal controller is in signal communication with thequasi-resonant auto-tuning controller. The mixed-signal controller isconfigured to receive the valley point signal and, in response, producea pulse width modulated (“PWM”) signal. A gate-driver drives the mainswitch and is in signal communication with the main switch andmixed-signal controller. The gate-driver is configured to receive thePWM signal and produce a gate-driver signal.

Other devices, apparatuses, systems, methods, features, and advantagesof the invention will be or will become apparent to one with skill inthe art upon examination of the following figures and detaileddescription. It is intended that all such additional devices,apparatuses, systems, methods, features, and advantages be includedwithin this description, be within the scope of the invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be better understood by referring to the followingfigures. In the figures, like reference numerals designate correspondingparts throughout the different views.

FIG. 1 is a schematic diagram of an example flyback converter, inaccordance with the present disclosure.

FIG. 2 is a schematic diagram of an example quasi-resonant auto-tuningcontroller shown in FIG. 1 , in accordance with the present disclosure.

FIG. 3A is a plot of an example auxiliary signal produced by theauxiliary-winding, shown in FIG. 1 , in accordance with the presentdisclosure.

FIG. 3B is a plot of an example offset auxiliary signal produced by thezero-voltage crossing detection circuit, shown in FIG. 2 , in accordancewith the present disclosure.

FIG. 3C is a plot of an example comparison signal produced by thezero-voltage crossing detection circuit, shown in FIG. 2 , in accordancewith the present disclosure.

FIG. 3D is a plot of an example valley point signal produced by thequasi-resonant auto-tuning controller, shown in FIGS. 1 and 2 , inaccordance with the present disclosure.

FIG. 4 is a flowchart illustrating a portion of an example process foroperation of the quasi-resonant auto-tuning controller shown in FIGS. 1and 2 , in accordance with the present disclosure.

DETAILED DESCRIPTION

In the following description, like reference numbers are used toidentify like elements. Furthermore, the drawings are intended toillustrate major features of example embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of actualembodiments.

Disclosed herein is a quasi-resonant auto-tuning controller of a flybackconverter for accurate detection of voltage valley points duringquasi-resonant operation across a wide range of input voltages (forexample, between 85 to 265 volts), across a wide range of outputvoltages (for example, between 3 to 24 volts), and across a wide rangeof output load current operating conditions.

Accurate detection of voltage valley points (i.e., local voltage minima)of a quasi-resonant signal is often desirable for quasi-resonantoperation in a flyback converter. This is because during quasi-resonantoperation of the flyback converter, a primary-side switch (“mainswitch”) of the flyback converter is ideally switched when a drainvoltage of the main switch is at a minimum. Switching the main switchwhen a drain voltage of the switch is at a minimum improves powerprocessing efficiency, reduces voltage stress across semiconductorswitches, and reduces electromagnetic interference. However, at presentit is often difficult to accurately detect main switch drain voltagevalley points of a flyback converter operating in quasi-resonantconduction mode across a wide range of flyback converter input voltages(for example, from 85 VAC to 265 VAC), output voltages (for example,from 3 VDC to 24 VDC), and across varying output loads.

Some known related approaches typically require manual tuning byutilizing external components. Such known approaches are sensitive toquasi-resonant period variations due to variations in the input andoutput voltages of the flyback converter.

In order to accurately turn-on the main switch at a valley point acrossvarying input and output conditions, and in the presence of systemdelays such as gate-driver propagation, valley detector conversion andprocessing delays, and a variable quasi-resonant period (for example,between approximately 800 ns to 2500 ns), an adaptive/predictive valleydetection method is disclosed herein.

As a result of accurately detecting the voltage valley points, thequasi-resonant auto-tuning controller allows for optimal implementationof quasi-resonant operation of the flyback converter by switching themain switch of the flyback converter when the drain voltage of the mainswitch is minimum. Resultantly, the quasi-resonant auto-tuningcontroller allows for improved AC-to-DC power conversion efficiency,reduced voltage stress across semiconductor switches, and reducedelectromagnetic interference. Moreover, the quasi-resonant auto-tuningcontroller accomplishes these goals without the need for manual tuningof external components or sensitivity to quasi-resonant periodvariations.

In general, the principle of operation of the quasi-resonant auto-tuningcontroller involves measuring a half-period of the multiple oscillationripples of a quasi-resonant signal using an auxiliary signal produced byan auxiliary winding of the flyback converter. The half-period ismeasured using a zero-voltage crossing detection circuit of aprimary-side controller. The detected quasi-resonant half-periods areconverted to quarter-periods (i.e., divided pulse widths) and stored ina look-up table (LUT) (e.g., in a memory device). In this example, eachquarter-period of the oscillation ripples corresponds to valley points(i.e., a first valley point, a second valley point, a third valleypoint, etc.) of the oscillation ripples. During a subsequent switchingcycle of the flyback converter, when the quasi-resonant auto-tuningcontroller detects a zero-voltage crossing for a desired valley at whichto switch (i.e., at a first valley, a second valley, a third valley,etc.), the quasi-resonant auto-tuning controller waits for a measuredone quarter-period before producing a valley point signal thatrepresents an estimated valley point of the corresponding oscillationripple of the auxiliary signal (i.e., the quasi-resonant signal). If theflyback converter is exclusively switching at a first valley of thequasi-resonant signal, it may not be possible for the quasi-resonantauto-tuning controller to measure a full quasi-resonant half-period.Thus, in some examples, if the quasi-resonant auto-tuning controllerdetermines that the main switch of the flyback converter has beenexclusively switching at a first valley point of the quasi-resonantsignal for a threshold number of previous switching cycles of theflyback converter, the quasi-resonant auto-tuning controller is operableto force the flyback converter to switch at a second (or later) valleypoint of the quasi-resonant signal for one or more subsequent switchingcycles periodically to measure the quasi-resonant half-period. Forexample, the quasi-resonant auto-tuning controller may force the flybackconverter to switch at the second valley point of the quasi-resonantsignal for one or more switching cycles once every 255 switching cyclesupon determining that flyback converter has been switching exclusivelyat the first valley point of the quasi-resonant signal for the preceding255 switching cycles.

Turning to FIG. 1 , a schematic diagram is shown of an exampleimplementation of a primary-side controller 100 of a flyback converter102, in accordance with the present disclosure. In operation, theflyback converter 102 receives an input voltage (“V_(In)”) 142 andproduces an output voltage (“V_(Out)”) 144. In this example, theprimary-side controller 100 includes a quasi-resonant auto-tuningcontroller 104, a mixed-signal controller 106, and a gate-driver 108.The mixed-signal controller 106 is in signal communication with both thequasi-resonant auto-tuning controller 104 and the gate-driver 108.

In this example, the flyback converter 102 includes a primary-sidecircuit 110, a secondary-side circuit 112, and an auxiliary circuit 148.The auxiliary circuit 148 generally includes an auxiliary-winding 150 ofa transformer 114, an auxiliary ground 152, a first voltage dividerresistor 154, a second voltage divider resistor 156, a series diode 158,a voltage regulator (e.g., an LDO) 160, and capacitors 162, 164. Theprimary-side circuit 110 and secondary-side circuit 112 are in signalcommunication via the transformer 114 having a primary-winding 116, asecondary-winding 118, the auxiliary-winding 150, and a core 120. Theprimary-winding 116 is part of the primary-side circuit 110, and thesecondary-winding 118 is part of the secondary-side circuit 112. Theprimary-side circuit 110 includes the main switch 122, a current-senseresistor 134, and a snubber circuit which includes a resistor 128, acapacitor 130, and a diode 132. Also shown is a representation of amagnetizing inductance 124 and a representation of a parasiticinductance 126 of the transformer 114. The primary-winding 116, thecapacitor 130, and the diode 132 are in signal communication with adrain 136 of the main switch 122. The current-sense resistor 134 is insignal communication with a source 138 of the main switch 122 and aprimary-side ground 140. In this example, the main switch 122 is afield-effect transistor (“FET”) that may be a metal-oxide semiconductorfield-effect transistor (“MOSFET”).

The primary-side controller 100 is in signal communication with theauxiliary circuit 148, the main switch 122, and the voltage input of theprimary-side circuit 110. In particular, a gate 146 of the main switch122 is in signal communication with the gate-driver 108. Theprimary-side controller 100 receives the input voltage V_(In) 142, avoltage V_(sns) 191 that is representative of a current through the mainswitch 122, a feedback signal 190, an operating voltage 193, and anauxiliary signal 196 from the auxiliary-winding 150. The primary-sidecontroller 100 is in signal communication with the voltage regulator 160to receive the operating voltage 193 and the voltage divider resistors154 and 156 to receive the auxiliary signal 196.

The primary-side controller 100 is also in signal communication with anoptocoupler 180. In this example, feedback from the secondary-sidecircuit 112 to the primary-side circuit 110 is provided by theoptocoupler 180 in combination with a Zener diode 182 and a resistivenetwork that includes first, second, third, and fourth resistors 183,184, 185, and 186, respectively. The optocoupler 180 includes an LED 187and a phototransistor 188. The phototransistor 188 is in signalcommunication with the primary-side controller 100 and ground 189. Inoperation, the optocoupler 180 provides a feedback signal 190 to theprimary-side controller 100 that indicates whether more or less powerneeds to be transferred from the primary-side circuit 110 to thesecondary-side circuit 112 through the transformer 114.

The secondary-side circuit 112 includes the secondary-winding 118, asecondary-side switch 166, a capacitor 168, secondary-side ground 170,and a secondary-side controller 172. The secondary-side controller 172is in signal communication with a gate 174, drain 176, and source 178 ofthe secondary-side switch 166 and the secondary-side ground 170. In thisexample, the secondary-side switch 166 may also be a FET such as aMOSFET. The secondary-side controller 172 is also configured to receiveV_(Out) 144.

In an example of operation, the mixed-signal controller 106 controls theoperation of the main switch 122 by producing a pulse width modulated(“PWM”) signal 192 that is passed to the gate-driver 108. The PWM signal192 is received by the gate-driver 108 and converted into a drivingvoltage signal 194 that is injected into the gate 146 of the main switch122 and turns on or off the main switch 122. A sequence of turning onthe main switch 122 and turning off the main switch 122 is considered tobe a switching cycle of the flyback converter 102. The gate-driver 108may be a circuit, device, or component that includes circuitry toconvert the PWM signal 192, which is a digital signal, to the drivingvoltage signal 194 capable of driving the main switch 122. In thisexample, the PWM signal 192 is also passed to the quasi-resonantauto-tuning controller 104. The quasi-resonant auto-tuning controller104 utilizes the PWM signal 192 as a valley detection reset trigger. Thequasi-resonant auto-tuning controller 104 receives the auxiliary signal196 from the auxiliary-winding 150 through the voltage divider resistors154 and 156. In response, the quasi-resonant auto-tuning controller 104produces a valley point signal 198 (i.e., a signal indicating that avalley has occurred) that is passed to the mixed-signal controller 106.The mixed-signal controller 106 then utilizes the valley point signal198 to determine when the main switch 122 should be switched. It isappreciated by those of ordinary skill in the art that in designing aswitched-mode power supply, designers seek to maximize efficiency of theswitched-mode power supply by attempting to switch the main switch 122when a voltage between the drain and the source (“V_(DS)”) is at avoltage valley (i.e., at a minimum voltage level). As such, themixed-signal controller 106 optimizes a switching time of the mainswitch 122 to occur at a valley point.

In FIG. 2 , a schematic diagram is shown of an example of animplementation of the quasi-resonant auto-tuning controller 104, inaccordance with the present disclosure. In this example, thequasi-resonant auto-tuning controller 104 includes a zero-voltagecrossing detection circuit 200 in signal communication with a valleytuning finite-state machine 202. The zero-voltage crossing detectioncircuit 200 includes a comparison circuit 204, a first voltage dividernetwork 206, a second voltage divider network 208, and a seriescapacitor 210. The comparison circuit 204 may be implemented as anoperational amplifier (“op-amp”) that includes an inverting terminal 212and a non-inverting terminal 214. The first voltage divider network 206includes voltage divider resistors 216, 218 coupled to a ground node220. The second voltage divider network 208 includes voltage dividerresistors 222, 224 coupled to the ground node 220. In this example, thevoltage divider resistors 216, 218 of the first voltage divider network206 and the series capacitor 210 are in signal communication with theinverting terminal 212 of the comparison circuit 204. The voltagedivider resistors 222, 224 of the second voltage divider network 208 arein signal communication with the non-inverting terminal 214 of thecomparison circuit 204. An output terminal 226 of the comparison circuit204 is in signal communication with the valley tuning finite-statemachine 202.

The valley tuning finite-state machine 202 is a finite-state machine(also known as a “state machine”) which is a device that can be inexactly one of a finite number of states at any given time. Afinite-state machine may change from one state to another in response toexternal inputs and is defined by a list of its states, its initialstate, and the conditions for each transition (i.e., the change from onestate to another). The valley tuning finite-state machine 202 may beimplemented as a digital circuit that may include a programmable logicdevice, programmable logic controller, logic gates and flip-flops orrelays. As an example, the valley tuning finite-state machine 202 mayinclude a register to store state variables, a block of combinationallogic that determines the state transitions, and a second block ofcombinational logic that determines the output of the valley tuningfinite-state machine 202.

In this example, the valley tuning finite-state machine 202 includes apulse-width look-up table (“LUT”) 228, and combinational logic circuitry(“logic circuit”) 234, connected as shown. A simplified exampleoperational view 235 of the combinational logic circuitry 234 is alsoshown to illustrate generation of the valley point signal(“ValleyPoint”) 198.

At a high level, the valley tuning finite-state machine 202 measures aduration of a half-period of a quasi-resonant waveform present at adrain node of the main switch 122 of the flyback converter 102. Thevalley tuning finite-state machine 202 uses the measured half-period(i.e., a half-pulse width) to determine a quarter-period (i.e., adivided pulse width) ¼T_(QRperiod)(n) of the quasi-resonant waveform(e.g., using a divider circuit), and stores each duration correspondingto the quarter-period in the pulse-width LUT 228. The next time that azero crossing of the quasi-resonant waveform is detected, (i.e., duringa subsequent switching cycle of the flyback converter 102), the valleytuning finite-state machine 202 waits for a duration of time(¼T_(QRperiod)(n)) corresponding to a stored duration in the pulse-widthLUT 228 (i.e., a duration corresponding to a previously determinedquarter-period) before issuing a valley point signal. The valley pointsignal (ValleyPoint 198) is used by the mixed-signal controller 106 tocontrol a switching time for the main switch 122 such that a voltage atthe drain node of the main switch 122 is at a voltage minimumcorresponding to a desired valley of the quasi-resonant waveform. Forexample, if during a subsequent switching cycle, upon determining that azero-crossing corresponding to a desired valley at which to switch(e.g., a first valley, a second valley, a third valley, etc.) hasoccurred, the valley tuning finite-state machine 202 waits a duration oftime corresponding to the determined valley point before issuing avalley point signal (ValleyPoint 198).

In this example, the pulse-width LUT 228 is a look-up table within amemory module, programmable logic circuit, or another component. Thelogic circuit 234 is operable to determine a pulse width (e.g., using acounter circuit block), divide the determined pulse width (e.g., using adivider circuit block), generate a delayed pulse (e.g., using a delaycircuit block), as well as being operable to perform other operations.

For example, the logic circuit 234 is operable to count a length of timethat corresponds to the pulse width of each pulse of the multiple pulsesof a comparison signal (“compQr”) 236 produced by the comparison circuit204.

During operation of the flyback converter 102, an induced currentdevelops at the auxiliary-winding 150, thereby producing an auxiliaryvoltage Vaux(t) 195 across the auxiliary-winding 150. The auxiliaryvoltage Vaux(t) 195 is divided down by the voltage divider resistors154, 156 (shown in FIG. 1 ) to produce an auxiliary signal 196 which isreceived by the zero-voltage crossing detection circuit 200. The seriescapacitor 210 (shown in FIG. 2 ) eliminates any DC component of theauxiliary signal 196. The first voltage divider network 206 offsets theremaining AC component of the auxiliary signal 196 with a DC componentproduced from a source voltage (“V_(CC)”) 242 (e.g., the operatingvoltage 193) to produce an offset auxiliary signal 244 that is passed tothe inverting terminal 212 of the comparison circuit 204. The offsetauxiliary signal 244 (“VauxOffset”) can be expressed as;VauxOffset=H×Vaux(t)+V _(DC)  (Equation 1)where H is a scalar produced by the voltage divider resistors 154,156and 216, 218, Vaux(t) is the auxiliary voltage Vaux(t) 195 generated bythe auxiliary-winding 150, and V_(DC) is an offset voltage generated bydividing V_(CC) 242 by the first voltage divider network 206. Theresultant offset auxiliary signal VauxOffset 244 is received at theinverting terminal 212 of the comparison circuit 204.

The second voltage divider network 208 divides V_(CC) 242 by voltagedivider resistors 222, 224 to generate a comparison reference signal 246having the DC voltage value V_(DC). The comparison reference signal 246is received at the non-inverting input of the comparison circuit 204.The comparison circuit 204 compares signals received at the invertingand non-inverting terminals 212, 214 of the comparison circuit 204 togenerate the comparison signal compQr 236. Thus, in instances whereV_(CC) 242 may fluctuate, both the DC offset of VauxOffset 244 and theDC voltage level of the comparison reference signal 246 will fluctuatecorrespondingly.

In this example, the AC component of the auxiliary signal 196 includes aseries of oscillation ripples of a quasi-resonant waveform, whereby eachoscillation ripple of the series of oscillation ripples has a peak pointand valley point. It is appreciated by those of ordinary skill in theart that such oscillation ripples in the auxiliary signal 196 are theresult of quasi-resonant oscillations at the drain 136 (i.e., V_(DS)) ofthe main switch 122. Such oscillations are caused by parasiticinductances and capacitances of the circuitry in the flyback converter102.

In some embodiments, the voltage divider resistor 216 has a resistancevalue that is equal to a resistance value of the voltage dividerresistor 222. Similarly, in such embodiments, the voltage dividerresistor 218 has a resistance value that is equal to a resistance valueof the voltage divider resistor 224. As such, a DC voltage value V_(DC)of the comparison reference signal 246 is equal to a DC offset valueV_(DC) of the offset auxiliary signal 244. Moreover, an AC component ofthe offset auxiliary signal 244 alternates above and below V_(DC) suchthat V_(DC) may be considered a “zero-reference” for the offsetauxiliary signal 244. As such, when the AC component of the offsetauxiliary signal 244 transitions from a voltage level above V_(DC) to avoltage level below V_(DC) or from a voltage level below V_(DC) to avoltage level above V_(DC) the transition is considered a“zero-crossing.”

The comparison circuit 204 compares the offset auxiliary signal 244against the comparison reference signal 246 to produce the comparisonsignal compQr 236. The comparison signal compQr 236 is a digital signalthat has a positive pulse (i.e., a digital 1) if the offset auxiliarysignal 244 has a voltage value that is less than or equal to thecomparison reference signal 246 and no pulse (i.e., a digital 0) if theoffset auxiliary signal 244 has a voltage value that is greater than thecomparison reference signal 246. The comparison signal compQr 236 isreceived by both the pulse-width LUT 228 and the logic circuit 234. Inthis example, pulses of the comparison signal compQr 236 havepulse-width durations that correspond to a half-period of theoscillation ripples of the offset auxiliary signal 244. Thiscorrespondence occurs because each pulse of the comparison signal compQr236 pulse begins when the oscillation ripple causes the voltage value ofthe offset auxiliary signal 244 to drop to, or below, the comparisonreference signal 246 (i.e., V_(DC)) and ends when the oscillation ripplecauses the voltage value of the offset auxiliary signal 244 to riseabove the comparison reference signal 246.

The pulse-width LUT 228 uses the pulse duration of the comparison signalcompQr 236 to determine and store a duration of time corresponding to aquarter-period of the oscillation ripples of the offset auxiliary signal244 (i.e., half of the half-period duration of the oscillation ripple).Each quarter-period of the offset auxiliary signal 244 corresponds to anestimated position of a voltage minimum (i.e., a valley) of the offsetauxiliary signal 244 (i.e., a first valley, a second valley, a thirdvalley, etc.)

The next time a valley is detected, in a subsequent switching cycle ofthe flyback converter 102, the logic circuit 234 sends a valleydetection signal valley(n) 240 to the pulse-width LUT 228. Thepulse-width LUT 228 transmits a delay value ¼T_(QRperiod)(n) 238 to thelogic circuit 234. After a duration of time corresponding to¼T_(QRperiod)(n) from the valley detection signal valley(n) 240, thelogic circuit 234 transmits a valley point (“ValleyPoint”) 198 signal tothe mixed-signal controller 106 which switches the main switch 122 basedon the valley point signal 198. Valley point detection is reset by thelogic circuit 234 upon receiving a subsequent PWM signal 192. In someembodiments, if the quasi-resonant auto-tuning controller 104 determinesthat the main switch 122 of the flyback converter 102 has beenexclusively switching at a first valley point of the quasi-resonantsignal for a threshold number of previous switching cycles (e.g., 63switching cycles, 127 switching cycles, 255 switching cycles, 511switching cycles, etc.) of the flyback converter 102, the quasi-resonantauto-tuning controller 104 is operable to force the flyback converter102 to switch at a second (or later) valley point of the quasi-resonantsignal for one or more subsequent switching cycles to measure thequasi-resonant half-period. In some embodiments, determining, by thequasi-resonant auto-tuning controller 104, that the flyback converter102 has been exclusively switching at a first valley point of thequasi-resonant signal for a threshold number of previous switchingcycles of the flyback converter 102 is performed by the valley tuningfinite-state machine 202. In some such embodiments, determining, by thequasi-resonant auto-tuning controller 104, that the flyback converter102 has been exclusively switching at a first valley point of thequasi-resonant signal for a threshold number of previous switchingcycles of the flyback converter 102 is performed by the combinationallogic circuitry 234.

Turning to FIG. 3A, a plot 300 of an example auxiliary voltageV_(aux)(t) 195 produced by the auxiliary-winding 150 is shown inaccordance with the present disclosure. The plot 300 of the auxiliaryvoltage V_(aux)(t) 195 is graphed as voltage versus time, where the plot300 varies from a low voltage −V_(in)/tr_(vin) to a high voltageV_(out)/tr_(aux), where tr_(vin) is a primary-to-secondary turns ratioof the transformer 114, and tr_(aux) is an auxiliary-to-secondary turnsratio of the transformer 114. In this example, auxiliary voltageV_(aux)(t) 195 is shown to have a first valley point 310, a secondvalley point 312, a third valley point 313, a first peak 314, and asecond peak 316. The oscillation ripples of the auxiliary signal 196vary between the high voltage V_(out)/tr_(aux) and a second low voltage−V_(out)/tr_(aux). The first valley point 310 has a voltage value equalto −V_(out)/tr_(aux). Because the oscillations of the auxiliary voltageV_(aux)(t) 195 are damped, the subsequent oscillation ripples will havevalley points that are greater than the second low voltage−V_(out)/tr_(aux) and peaks that are less than the high voltageV_(out)/tr_(aux).

In this example, the auxiliary voltage V_(aux)(t) 195 starts at the lowvoltage −V_(in)/tr_(vin) that is less than 0 and then rises to highvoltage V_(out)/tr_(aux) after the main switch 122 is turned off. Theauxiliary voltage V_(aux)(t) 195 transitions across a 0V level at afirst time t₁ and then drops to the second low voltage −V_(out)/tr_(aux)by again crossing the 0V level at a second time t₂. The auxiliaryvoltage V_(aux)(t) 195 reaches the second low voltage −V_(out)/tr_(aux)at a third time t₃ that corresponds to the first valley point 310. Theauxiliary voltage V_(aux)(t) 195 then rises again to approximately thehigh voltage V_(out)/tr_(aux) by crossing the 0V level at a fourth timet₄. The auxiliary voltage V_(aux)(t) 195 then drops again to the secondvalley point 312 by crossing the 0V level at a fifth time t₅. Theauxiliary voltage V_(aux)(t) 195 then rises again to a voltage below thehigh voltage V_(out)/tr_(aux) by crossing the 0V level at a sixth timet₆. The auxiliary voltage V_(aux)(t) 195 then drops again by crossingthe 0V level at a seventh time t₇. At an eighth time t₈, the main switch122 is turned on and the auxiliary voltage V_(aux)(t) 195 returns to thelow voltage −V_(in)/tr_(vin).

In FIG. 3B, a plot 336 of an example offset auxiliary signal VauxOffset244 produced by the zero-voltage crossing detection circuit 200 is shownin accordance with the present disclosure. The plot 336 of the offsetauxiliary signal VauxOffset 244 is graphed as a voltage versus time. Asdiscussed earlier, the offset auxiliary signal VauxOffset 244 has thesame waveform shape as the auxiliary voltage V_(aux)(t) 195, thoughhaving an attenuated amplitude and a DC offset V_(DC). As such, theoffset auxiliary signal VauxOffset 244 varies above and below the DCoffset V_(DC) instead of above and below 0V. In this disclosure, thecrossing of the DC offset V_(DC) by the offset auxiliary signalVauxOffset 244 is still considered to be a zero-crossing because itcorresponds to the actual zero-crossing of the auxiliary voltageV_(aux)(t) 195 produced by the auxiliary-winding 150. In this example,the zero-crossings of the offset auxiliary signal 244 VauxOffset occurat the same times as the zero-crossings of the auxiliary voltageV_(aux)(t) 195.

In FIG. 3C, a plot 340 is shown of an example comparison signal compQr236 produced by the zero-voltage crossing detection circuit 200 inaccordance with the present disclosure. The plot 340 of the comparisonsignal compQr 236 is graphed as a logic value (i.e., a digital 1 or 0)versus the same time span shown in FIGS. 3A and 3B. In this example, thecomparison signal compQr 236 includes a first pulse 344, a second pulse346, a third pulse 348, and a fourth pulse 350. The first pulse 344corresponds to a comparison (by the comparison circuit 204) indicatingthat the offset auxiliary signal 244 is less than V_(DC) before t₁. Thesecond pulse 346 corresponds to a comparison indicating that the offsetauxiliary signal 244 is less than V_(DC) between t₂ and t₄. The thirdpulse 348 corresponds to a comparison indicating that the offsetauxiliary signal 244 is less than V_(DC) between t₅ and t₆, and thefourth pulse 350 corresponds to a comparison indicating that the offsetauxiliary signal 244 is less than V_(DC) after t₇. In this example, thesecond pulse 346 has a first pulse-width 352 that corresponds to a firsthalf-period 354 of the first valley (shown in FIG. 3A) and the thirdpulse 348 has a second pulse-width 356 that corresponds to a secondhalf-period 358 of the second valley (shown in FIG. 3A). In thisexample, the first quarter-period 360 corresponds to half of the firstpulse-width 352, and the second quarter-period 362 corresponds to halfof the second pulse-width 356. The first valley point 310 is located afirst quarter-period 360 (i.e., a first divided pulse width) away fromt₂ and the second valley point 312 is located a second quarter-period362 (i.e., a second divided pulse width) away from t₅. In this example,the main switch 122 turns on at a third quarter-period 364 (at the thirdvalley point 313) away from t₇.

Turning to FIG. 3D, a plot 366 of the valley point signal(“ValleyPoint”) 198 produced by the quasi-resonant auto-tuningcontroller 104 is shown in accordance with the present disclosure. Theplot 366 of the valley point signal 198 is graphed as a logic value(e.g., a digital 1 or 0) versus the same time span shown in FIGS. 3Athrough 3C.

The plot 366 of the valley point signal 198 shows a first pulse 370,second pulse 372, and third pulse 374. The three pulses 370, 372, and374 are shorter than the three pulses 346, 348, and 350 for thecomparison signal compQr 236 and start at the quarter-period times ofthe offset auxiliary signal VauxOffset 244. That is, the first pulse 370starts at the first quarter-period 360 away from t₂, the second pulse372 starts at the second quarter-period 362 away from t₅, and the thirdpulse 374 starts at the third quarter-period 364 away from t₇. As such,the first pulse 370, the second pulse 372, and the third pulse 374correspond to the true first valley point 310, second valley point 312,and third valley point 313, respectively.

FIG. 4 is a flowchart illustrating a portion of an example process 400of operation of the quasi-resonant auto-tuning controller 104 inaccordance with the present disclosure. The process 400 starts byreceiving 402 the offset auxiliary signal VauxOffset 244 from theauxiliary-winding 150 and the comparison reference signal 246. Asdiscussed earlier, the offset auxiliary signal VauxOffset 244 includes aseries of oscillation ripples (i.e., a quasi-resonant signal), whereeach oscillation ripple of the series of oscillation ripples has a peakpoint and valley point. The process 400 then compares 404 the offsetauxiliary signal VauxOffset 244 against the comparison reference signal246 to produce the comparison signal compQr 236 that includes a seriesof pulses when the offset auxiliary signal VauxOffset 244 is less thanthe comparison reference signal 246, where each pulse of the series ofpulses has a pulse width that corresponds to a half-period of anoscillation ripple of the series of oscillation ripples. As discussedearlier, the offset auxiliary signal 244 is related to the auxiliarysignal 196 with a DC offset Vic and gain/attenuation factor H. Theprocess 400 then determines 406 the pulse width of each pulse of theseries of pulses of the comparison signal compQr 236, produces 408 adivided pulse width from each pulse width, where the divided pulse widthcorresponds to a quarter-period of the oscillation ripple, i.e., half ofthe pulse width, and then stores 410 the divided pulse width of eachpulse in the pulse-width LUT 228. In a subsequent switching cycle, theprocess 400 then determines 412, using the comparison signal, that theoffset auxiliary signal 244 is less than the comparison reference signal246 (i.e., another valley has been detected, for example in a subsequentswitching cycle of the main switch 122). If the offset auxiliary signal244 is not less than the comparison reference signal 246, the process400 repeats steps 402 through 412. If, instead, the offset auxiliarysignal 244 is less than the comparison reference signal 246 (i.e.,corresponding to a desired valley during a subsequent switching cycle),the process 400 waits 414 a time period that corresponds to thequarter-pulse width stored in the pulse-width LUT 228. The process 400then produces 416 the valley point signal 198 after waiting the timeperiod and the process 400 repeats.

In this example, the step of producing 404 the comparison signal compQr236 includes sub-steps that include removing the DC voltage from theauxiliary signal 196 with the series capacitor 210, adding the referencevoltage to produce the offset auxiliary signal 244, and producing thecomparison signal compQr 236 by comparing the offset auxiliary signalVauxOffset 244 against the comparison reference signal 246. As discussedearlier, the comparison signal compQr 236 includes the series of pulsesindicating when the offset auxiliary signal VauxOffset 244 is less thanthe comparison reference signal 246. Furthermore, the step ofdetermining 406 the pulse width includes counting a length of time thatcorresponds to the pulse width of each pulse of the series of pulses ofthe comparison signal compQr 236, where the length of time correspondsto the half-period of the oscillation ripple. Moreover, the step ofproducing 408 a divided pulse width includes dividing each pulse widthby two to produce the divided pulse width, where the divided pulse widthcorresponds to the quarter-period of the oscillation ripple.

It is appreciated by those skilled in the art that the circuits,components, modules, and/or devices of, or associated with, theprimary-side controller 100, the flyback converter 102, and thequasi-resonant auto-tuning controller 104 are described as being insignal communication with each other, where signal communication refersto any type of communication and/or connection between the circuits,components, modules, and/or devices that allows a circuit, component,module, and/or device to pass and/or receive signals and/or informationfrom another circuit, component, module, and/or device. Thecommunication and/or connection may be along any signal path between thecircuits, components, modules, and/or devices that allows signals and/orinformation to pass from one circuit, component, module, and/or deviceto another and includes wireless or wired signal paths. The signal pathsmay be physical, such as, for example, conductive wires, electromagneticwaveguides, cables, attached and/or electromagnetic or mechanicallycoupled terminals, semi-conductive or dielectric materials or devices,or other similar physical connections or couplings. Additionally, signalpaths may be non-physical such as free-space (in the case ofelectromagnetic propagation) or information paths through digitalcomponents where communication information is passed from one circuit,component, module, and/or device to another in varying digital formatswithout passing through a direct electromagnetic connection.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention. It isnot exhaustive and does not limit the claimed inventions to the preciseform disclosed. Furthermore, the foregoing description is for thepurpose of illustration only, and not for the purpose of limitation.Modifications and variations are possible in light of the abovedescription or may be acquired from practicing the invention. The claimsand their equivalents define the scope of the invention.

In some alternative examples of implementations, the function orfunctions noted in the blocks may occur out of the order noted in thefigures. For example, in some cases, two blocks shown in succession maybe executed substantially concurrently, or the blocks may sometimes beperformed in the reverse order, depending upon the functionalityinvolved. Also, other blocks may be added in addition to the illustratedblocks in a flowchart or block diagram.

The description of the different examples of implementations has beenpresented for purposes of illustration and description and is notintended to be exhaustive or limited to the examples in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different examples ofimplementations may provide different features as compared to otherdesirable examples. The example, or examples, selected are chosen anddescribed to best explain the principles of the examples, the practicalapplication, and to enable others of ordinary skill in the art tounderstand the disclosure for various examples with variousmodifications as are suited to the particular use contemplated.

Moreover, reference has been made in detail to examples ofimplementations of the disclosed invention, one or more examples ofwhich have been illustrated in the accompanying figures. Each examplehas been provided by way of explanation of the present technology, notas a limitation of the present technology. While the specification hasbeen described in detail with respect to specific examples ofimplementations of the invention, it will be appreciated that thoseskilled in the art, upon attaining an understanding of the foregoing,may readily conceive of alterations to, variations of, and equivalentsto these examples of implementations. For instance, features illustratedor described as part of one example of an implementation may be usedwith example of another implementation to yield a still further exampleof an implementation. Thus, it is intended that the present subjectmatter covers all such modifications and variations within the scope ofthe appended claims and their equivalents. These and other modificationsand variations to the present invention may be practiced by those ofordinary skill in the art, without departing from the scope of thepresent invention, which is more particularly set forth in the appendedclaims. Furthermore, those of ordinary skill in the art will appreciatethat the foregoing description is by way of example only, and is notintended to limit the invention.

What is claimed is:
 1. A method comprising: producing, by aquasi-resonant auto-tuning controller of a primary side controller of aflyback converter, a valley point signal from an auxiliary signalproduced by an auxiliary winding of the flyback converter, thequasi-resonant auto-tuning controller being in signal communication withthe auxiliary winding; receiving, by a pulse width modulated (“PWM”)controller in signal communication with the quasi-resonant auto-tuningcontroller, the valley point signal; producing, by the PWM controller inresponse to receiving the valley point signal, a PWM signal; andreceiving, by a gate-driver for driving a main switch of the flybackconverter, the PWM signal, wherein the gate-driver is in signalcommunication with the main switch and the PWM controller; andproducing, by the gate-driver, a gate-driver signal based on the PWMsignal.
 2. The method of claim 1, further comprising: receiving, by thequasi-resonant auto-tuning controller, the PWM signal as a valley pointdetection reset signal.
 3. The method of claim 1, wherein: thequasi-resonant auto-tuning controller comprises: a zero-voltage crossingdetection circuit; and a valley tuning finite-state machine having alook-up table; and the method further comprises: receiving, by thezero-voltage crossing detection circuit, the auxiliary signal and areference voltage, wherein the auxiliary signal includes a plurality ofoscillation ripples, and wherein each oscillation ripple of theplurality of oscillation ripples has a peak point and valley point; andproducing, by the zero-voltage crossing detection circuit, a comparisonsignal that includes a plurality of pulses when the auxiliary signal isless than the reference voltage, wherein each pulse of the plurality ofpulses has a pulse width that corresponds to a half-period of anoscillation ripple of the plurality of oscillation ripples; determining,by the valley tuning finite-state machine, the pulse width of each pulseof the plurality of pulses of the comparison signal; producing, by thevalley tuning finite-state machine, a divided pulse width from eachpulse width, wherein the divided pulse width corresponds to aquarter-period of the oscillation ripple; storing, by the valley tuningfinite-state machine, the divided pulse width of each pulse in thelook-up table; determining, by the valley tuning finite-state machineusing the comparison signal, that the auxiliary signal is less than thereference voltage; waiting, by the valley tuning finite-state machine, atime period that corresponds to the divided pulse width stored in thelook-up table if the auxiliary signal is less than the referencevoltage; and producing, by the valley tuning finite-state machine, thevalley point signal after waiting the time period.
 4. The method ofclaim 3, further comprising: upon determining, by the quasi-resonantauto-tuning controller, that the main switch has exclusively switched ata first valley point of the plurality of oscillation ripples for athreshold number of previous switching cycles of the flyback converter,forcing, by the quasi-resonant auto-tuning controller, the flybackconverter to switch the main switch at a second valley point of theplurality of oscillation ripples for one or more subsequent switchingcycles.
 5. The method of claim 3, wherein: the zero-voltage crossingdetection circuit includes a series capacitor; and the method furthercomprises: removing, by the zero-voltage crossing detection circuit, adirect current (“DC”) voltage from the auxiliary signal with the seriescapacitor; adding, by the zero-voltage crossing detection circuit, thereference voltage to the auxiliary signal to produce an offset auxiliarysignal; producing, by the zero-voltage crossing detection circuit, thecomparison signal by comparing the offset auxiliary signal against thereference voltage, wherein the comparison signal includes the pluralityof pulses when the offset auxiliary signal is less than the referencevoltage.
 6. The method of claim 5, wherein: the zero-voltage crossingdetection circuit comprises a comparison circuit in signal communicationwith the series capacitor; and the method further comprises: receiving,by the zero-voltage crossing detection circuit, the offset auxiliarysignal and the reference voltage; and producing, by the zero-voltagecrossing detection circuit using the comparison circuit, the comparisonsignal.
 7. The method of claim 3, wherein: the valley tuningfinite-state machine comprises: a storage device that includes thelook-up table; and a logic circuit; and the method further comprises:determining, by the logic circuit, a length of time that corresponds tothe pulse width of each pulse of the plurality of pulses of thecomparison signal, wherein the length of time corresponds to thehalf-period of the oscillation ripple; producing, by the logic circuit,the divided pulse width from each pulse width, wherein the divided pulsewidth corresponds to the quarter-period of the oscillation ripple;determining, by the logic circuit, that the auxiliary signal is lessthan the reference voltage; waiting, by the logic circuit, the timeperiod that corresponds to the divided pulse width stored in the look-uptable if the auxiliary signal is less than the reference voltage; andproducing, by the logic circuit, the valley point signal after waitingthe time period.
 8. The method of claim 7, wherein: the quasi-resonantauto-tuning controller, the PWM controller, and the gate-driver are allintegrated on a single integrated circuit.
 9. A flyback convertercomprising: a main switch; an auxiliary winding; and a primary sidecontroller comprising: a quasi-resonant auto-tuning controller in signalcommunication with the auxiliary winding, wherein the quasi-resonantauto-tuning controller is configured to produce a valley point signalfrom an auxiliary signal produced by the auxiliary winding; a pulsewidth modulated (“PWM”) controller in signal communication with thequasi-resonant auto-tuning controller, wherein the PWM controller isconfigured to receive the valley point signal and, in response, producea PWM signal; and a gate-driver for driving the main switch, wherein thegate-driver is in signal communication with the main switch and the PWMcontroller, and wherein the gate-driver is configured to receive the PWMsignal and produce a gate-driver signal.
 10. The flyback converter ofclaim 9, wherein: the quasi-resonant auto-tuning controller isconfigured to receive the PWM signal as a valley point detection resetsignal.
 11. The flyback converter of claim 9, wherein the quasi-resonantauto-tuning controller comprises: a zero-voltage crossing detectioncircuit; and a valley tuning finite-state machine having a look-uptable; wherein the zero-voltage crossing detection circuit is configuredto: receive the auxiliary signal and a reference voltage, wherein theauxiliary signal includes a plurality of oscillation ripples, andwherein each oscillation ripple of the plurality of oscillation rippleshas a peak point and valley point; and produce a comparison signal thatincludes a plurality of pulses when the auxiliary signal is less thanthe reference voltage, wherein each pulse of the plurality of pulses hasa pulse width that corresponds to a half-period of an oscillation rippleof the plurality of oscillation ripples; and wherein the valley tuningfinite-state machine is configured to: determine the pulse width of eachpulse of the plurality of pulses of the comparison signal; produce adivided pulse width from each pulse width, wherein the divided pulsewidth corresponds to a quarter-period of the oscillation ripple; storethe divided pulse width of each pulse in the look-up table; determine,using the comparison signal, that the auxiliary signal is less than thereference voltage; wait a time period that corresponds to the dividedpulse width stored in the look-up table if the auxiliary signal is lessthan the reference voltage; and produce the valley point signal afterwaiting the time period.
 12. The flyback converter of claim 11, wherein:upon determining, by the quasi-resonant auto-tuning controller, that themain switch has exclusively switched at a first valley point of theplurality of oscillation ripples for a threshold number of previousswitching cycles of the flyback converter, the quasi-resonantauto-tuning controller is configured to force the flyback converter toswitch the main switch at a second valley point of the plurality ofoscillation ripples for one or more subsequent switching cycles.
 13. Theflyback converter of claim 11, wherein: the zero-voltage crossingdetection circuit includes a series capacitor; the zero-voltage crossingdetection circuit is configured to remove a direct current (“DC”)voltage from the auxiliary signal with the series capacitor and then addthe reference voltage to produce an offset auxiliary signal; thezero-voltage crossing detection circuit produces the comparison signalby comparing the offset auxiliary signal against the reference voltage;and the comparison signal includes the plurality of pulses when theoffset auxiliary signal is less than the reference voltage.
 14. Theflyback converter of claim 13, wherein: the zero-voltage crossingdetection circuit comprises a comparison circuit in signal communicationwith the series capacitor; and the zero-voltage crossing detectioncircuit is configured to receive the offset auxiliary signal and thereference voltage and produce, using the comparison circuit, thecomparison signal.
 15. The flyback converter of claim 11, wherein: thevalley tuning finite-state machine comprises: a storage device thatincludes the look-up table; and a logic circuit configured to: determinea length of time that corresponds to the pulse width of each pulse ofthe plurality of pulses of the comparison signal, wherein the length oftime corresponds to the half-period of the oscillation ripple; producethe divided pulse width from each pulse width, wherein the divided pulsewidth corresponds to the quarter-period of the oscillation ripple;determine that the auxiliary signal is less than the reference voltage;wait the time period that corresponds to the divided pulse width storedin the look-up table if the auxiliary signal is less than the referencevoltage; and produce the valley point signal after waiting the timeperiod.
 16. The flyback converter of claim 15, wherein: thequasi-resonant auto-tuning controller, the PWM controller, and thegate-driver are all integrated on a single integrated circuit.